Lecture
This lecture discusses the importance of using a time coordinate associated with reference frames to satisfy Einstein's relativity principle. Two examples are presented: the speed of light and simultaneity, showing the relativity to the reference frame. The lecture explains the composition of velocities and introduces the concept of a time coordinate in the second reference frame. It also explores the concept of simultaneity and how it is relative to the reference frame, highlighting the impossibility of working with a single time coordinate.